This way, a Sliver has the Sliver Sense power, and thus is affected by the Sliver Sense Perception Area Enhanced Trait (here I used Blast, but given the variety of Sliver-ness that exists, it could be just about anything). The fact that the Perception Area targets Sliver Sense keeps non-Slivers from getting access to the power.

You could also just put Limited-only affects Slivers on the Collective Blast power. That way, any allies the Sliver's might have that aren't Slivers wouldn't get the bonus either, plus you wouldn't have to worry about enemies getting it.

That would probably work better most of the time. The thought behind the pairing of the special Perception Area and the special Sense was that it would give PCs a chance to "jam" Sliver collectives with Obscure type powers, or allow them to tap into the abilities being broadcast if they somehow developed or otherwise acquired Sliver Sense (Useful perhaps for Sliver/human hybrids or rogue free-thinking Sliver PCs).

Honestly, I don't think that this power perfectly represents Sliver abilities, but I did have a lot of coffee before I posted it, so I will irresponsibly shift the blame to that factor.